Insulation layer-forming compositions, also known as intumescent compositions, are customarily used to form coatings on the surface of building components in order to protect them against fire or against the effects of great heat, for example, as a result of a fire. Steel constructions are an integral part of modern architecture, even when they have a clear disadvantage compared to reinforced concrete. Above approximately 500° C., the load-bearing capacity of steel is reduced by 50%, i.e., steel loses most of its stability and its load-bearing capacity. This temperature may be reached, depending on the exposure to fire, for example, in the event of direct effect of fire (approximately 1000° C.) as rapidly as after 5 to 10 minutes, which often results in loss of load-bearing capacity of the construction. The objective of fire protection, in particular, of steel fire protection, is now to delay the loss of load-bearing capacity of a steel construction as long as possible in the event of a fire to save human lives and valuable objects.
For this reason, the construction regulations of many countries require specific fire resistance times of certain steel constructions. They are defined by so-called F classes such as F 30, F 60, F 90 (fire resistance classes according to DIN 4102-2) or U.S. classes according to ASTM, etc. For example, in DIN 4102-2, F 30, for example, means that, under standard conditions, a supporting steel structure must withstand fire for at least 30 minutes. This is customarily achieved by delaying the heating rate of steel, for example, by coating the steel construction using insulation layer-forming coatings. These are coatings whose components form a solid microporous carbon foam in the event of a fire. A thick foam layer having fine pores, known as ash crust, is then formed, which, depending on its composition, is highly heat-insulating, thus delaying the heating-up of the building component, so that the critical temperature of approximately 500° C. is not reached within 30, 60, 90, or 120 minutes, or up to 240 minutes. The layer thickness of the coat applied, i.e., the ash crust formed therefrom, is always important for the achievable fire-resistance. Closed profiles such as pipes, require approximately twice the amount of open profiles such as beams having a double T profile for a comparable mass. In order to comply with the required fire resistance times, the coatings must have a certain thickness and must be capable of forming, at impact of heat, an ash crust that is preferably voluminous and thus a good insulator, and that remains mechanically stable during the time of fire exposure.
Different systems exist in the prior art for this purpose. A difference is made basically between 100% systems and solvent-based or water-based systems. In solvent-based or water-based systems, binders, mostly resins, are applied to the building component as a solution, dispersion, or emulsion. These may be designed as single-component or multicomponent systems. After application, the solvent or water evaporates, leaving a film, which eventually dries. A distinction may be made between systems in which the coating is essentially no longer modified during drying, and systems in which, after evaporation, the binder cures primarily via oxidation or polymerization reactions induced, for example, by atmospheric oxygen. 100% systems contain the components of the binder without a solvent or water. They are applied to the building component, and “drying” of the coating takes place via reaction of the binder components with each other and/or via reaction with components of the ambient air, such as water.
Solvent-based or water-based systems have the disadvantage that drying times, also referred to as curing times, are long and also multiple layers must be applied, i.e., they require multiple operations to achieve the required layer thickness. Since each individual layer must dry before the next layer is applied, this results in long operating times and, therefore, high costs and delay in finishing the construction, since, depending on the climatic conditions, several days may pass before the required layer thickness is applied. It is also disadvantageous that, due to the required layer thickness, the coating may tend to form cracks and to flake during drying or impact of heat, whereby, in the worst case, the substrate may be partially exposed, in particular, in systems in which the binder is not post-cured after the solvent or water is evaporated.
In order to circumvent these disadvantages, epoxy-amine based two-component or multicomponent systems have been developed, which work almost without a solvent, so that curing occurs considerably faster and thicker layers may be applied in a single operation, so that the required layer thickness is built up substantially faster. However, they have the disadvantage that the binder forms a very stable and rigid polymer matrix often having an extended softening range, which hinders foam formation by the foaming agent. Therefore, thick layers must be applied in order to achieve sufficient foam thickness for insulation. This in turn is disadvantageous, since it requires large quantities of material. In order to make it possible to apply these systems, processing temperatures of up to +70° C. are often required, which makes these systems labor-intensive and expensive to install. Furthermore, some of the binder components used, such as amines or amine mixtures used in epoxy-amine systems, are toxic or otherwise critical (for example, irritating or corrosive).
In the area of decorative and protective coatings, the Michael addition is known as a curing mechanism. The reaction is customarily catalyzed by strong bases such as, for example, an amidine base. However, in formulations based on polymers, such as polyesters, which have hydrolytically cleavable bonds, it is disadvantageous that the coatings have reduced stability against hydrolysis. WO 2010/030771 A1, for example, describes a method for applying a curable composition onto a substrate, where curing takes place via Michael addition of a compound containing active hydrogen atoms to polyenes in the presence of a phosphine catalyst. Also in the area of adhesives, the Michael addition is known as a curing mechanism, as described, for example, in EP 1462501 A1.